The present invention is directed to a stator of an electrical machine, an electrical machine, and a power tool.
Electrical machines that are composed of a stator and a rotor, and that may be operated using alternating current or direct current, are also referred to as universal motors. Electric motors of this type are often used in household appliances and power tools, they may be powered by an alternating-current system, and a rectifier may also be used.
Increasingly greater energy densities are being required specifically of power tools, e.g., of angle grinders, since customers continually demand ever-smaller tools. The reduction in tool size should not necessarily require that the power also be reduced. Instead, reduced tool size should make it possible to increase the power. Basic limiting geometric conditions often makes this impossible, however.
With small angle grinders, for example, the electric motor is located directly in the user's grip region. The diameter of the electric motor is therefore particularly significant in this region, since it directly affects the diameter of the grip. Angle grinders typically have a further property that influences the grip shape and diameter, however. The tool is set into operation by actuating a pushbutton, and the switch-on motion takes place via a sliding switch that passes by the electric motor, in the rear region of the tool, in order to actuate an electrical switch that is located there inside the tool housing. To this end, the field core of the electric motor has a flat region in the axial direction on both sides of the field core. The housing in the grip region therefore encloses the electric motor, a sliding switch, and possibly an air gap between the electric motor and the housing, to ensure adequate cooling.
If the sliding switch is moved too closely to the field core, i.e., the laminated iron core, there is a risk that the field windings of the sliding switch could become jammed due to accumulation of dirt or deformation due to high temperature, thereby impairing or blocking the switch-on function—and, primarily, the switch-off function—of the device.
For this reason, two-pieced fields, i.e., a longitudinally divided field core with two core halves, have been provided, in the case of which the field core is separated in the pole separation. The field winding may be inserted in the core halves very easily and accurately, as a premanufactured coil or by winding the coil directly in place. The core halves are placed on top of each other before installation, and they are installed together with the motor housing. The two-pieced core is typically flat on the sides and makes it possible to obtain a much greater distance between the sliding switch and the field core than is possible with a one-pieced design. In the one-pieced design, the field core is composed of only one laminated core. The width of the field winding is greater than it is with a one-pieced field, however, with the disadvantage of higher losses in the field winding as compared with the one-pieced design.